Gas-Phase Catalytic Hydrogenation/Isomerization in the Transformation of 3-Butyn-2-ol over Pd-Ni/Al₂O₃

The continuous gas-phase (P = 1 atm; T = ₃₇₃ K) hydrogenation of 3-butyn-2-ol has been investigated over Pd/Al₂O₃ and Ni/Al₂O₃ prepared by incipient wetness impregnation and Pd–Ni/Al₂O₃ (Pd/Ni mol ratio = 1:1) synthesized by co-impregnation. A physical mixture (Pd/Al₂O₃ + Ni/Al₂O₃; Pd/Ni = 1:1) is also considered for comparison purposes. H₂ temperature-programmed reduction (TPR) results are consistent with a lower temperature requirement for the reduction of palladium and nickel in the bimetallic catalyst relative to the monometallic counterparts. The Pd/Al₂O₃ catalyst exhibits a narrow metal particle size distribution (mean = 20 nm) while Ni/Al₂O₃ and Pd–Ni/Al₂O₃ bore larger particles (mean = 28 ± 2 nm). TEM–EDX, XRD, and XPS measurements are consistent with a palladium surface-enriched Pd–Ni bimetallic phase. Ni/Al₂O₃ promoted exclusive −C≡C– group hydrogenation to generate 3-buten-2-ol (partial reduction) and 2-butanol (complete reduction). Pd/Al₂O₃ exhibited a greater H2 uptake and delivered a higher 3-butyn-2-ol transformation rate, yielding 3-buten-2-ol, 2-butanol, and 2-butanone through hydrogenation and double bond migration. An equivalent H₂ uptake, rate, and product distribution were delivered by Pd/Al₂O₃ and the Pd/Al₂O₃ + Ni/Al₂O₃ system, where the catalytic response was controlled by the palladium component. In contrast, we recorded a higher hydrogen chemisorption on Pd–Ni/Al₂O₃ (vs Pd/Al₂O₃) and catalytic activity with an enhanced selectivity to 3-buten-2-ol (up to 95%). We linked the distinct response over Pd–Ni/Al₂O₃ to the formation of bimetallic Pd–Ni as proven by TPR, XRD, TEM–EDX, and XPS analyses. A parallel/stepwise kinetic model has been used to quantify the catalytic hydrogenation response.